Optical glass



United States Patent 3,143,432 OPTICAL GLASS Heinz Briimer,Germannstein, and Norbert L. Meanert, Wetzlar (Lahn), Germany, assignorsto Ernst Leltz, G.m.b.H., Wetzlar (Latin), Germany, a corporation ofGermany No Drawing. Filed Jan. 6, 1960, Ser. No. 705 Claims priority,application Germany .i'an. 9, 1959 2 Olaims. (Cl. 10654) Our inventionrelates to optical glasses of high index of refraction and smalldispersion which are especially stable against chemicals and theatmosphere.

In co-pending application Serial No. 786,726, filed lanuary 14, 1959,optical glasses are described which consist of a glass base of silicondioxide, boron trioxide and lanthanum trioxide together with aluminumtrioxide and further with oxides used in the preparation of glass, inwhich the lanthanum oxide totals at least 20% by Weight and the borontrioxide at least 32% by weight of the total glass mix. Further in thisco-pending application there are described glasses of the abovementioned glass base and additional oxides in which the amount oflanthanum oxide shall amount to at least 40% by Weight.

Fu thermore, born-silicate glasses are known in the literature whichcontain greater amounts of lanthanum oxide as well as barium oxide.These last mentioned glasses are, however, very sensitive to spot ing orstaining so that their preparation and their use, particularly intropical districts, present serious difficulties.

Our present invention relates to glasses which are extraordinarilystable Without the use of aluminum oxide and which possess opticalvalues desired in glasses to be used in modern precision objectives. Theglasses may be very easily melted, are colorless, and present nodifliculties in their application and use. They are characterized inthat they contain between 20% and 46% by weight of silica and borontrioxide, of which the silica alone is between 14% and 35% by weight,between 30% and 40% by weight of lanthanum oxide as well as between 7.5%and 20% by weight of alkaline earth oxides, of which the amount ofbarium oxide is not to exceed by weight. To these glasses up to byweight of Zirconium oxide as well as up to 10% by weight of zinc oxideand/or cadmium oxide can be added. To adjust the optical values, up to10% by weight of the oxides of tantalum, niobium, lead, tungsten, andtitanium may be used additionally.

The amount of added barium oxide is to remain as low as possible sincethe barium oxide makes the glass soft and sensitive. Of the alkalineearth oxides, calcium is preferably to be used.

In the following table are shown some examples of the above glasses.

3,143,432 Patented Aug. 4, 1964 Table lMelt N0 Si 2 S1 5 I S1 8 I Si 3Si 7 Si 10 Si 21 The glasses are melted down in platinum vessels attemperatures between 1350 C. and 1500 C. They may be stirred to about1100 C. and cast in the usual manner.

Decolorizing substances, arsenic oxide, or stabilizing substances, asaluminum oxide may be added to the mixture in small amounts.

Having described our invention, we claim:

1. Optical glass with high index of refraction and small dispersionconsisting essentially of Percent by weight Silica and boron trioxide20-46 of which silica is 14-35 and the boron trioxide is not less than5.5 Lanthanum oxide 30-40 Alkaline earth oxide -20 of which barium oxideis less than .5 Zirconium oxide 0-10 at least one oxide of the groupconsisting of the oxides of zinc and cadmium 0-10 2. The optical glassof claim 1 containing additionally up to 10% by weight of at least oneoxide of the group consisting of tantalum, niobium, tungsten, lead, andtitanium.

References Cited in the file of this patent UNITED STATES PATENTS2,745,757 Geficken May 15, 1956 2,805,166 Lofller Sept. 3, 19572,899,322 Bromer et al. Aug. 11, 1959 3,006,776 Geffcken Oct. 31, 1961OTHER REFERENCES The Manufacture of Optical Glass and of OpticalSystems, 1921, pages and 132.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 3 l43432 August 4 19641 Heinz Brb'mer et a1 It is hereby certified that errorappears in the above numbered patent requiring correction and that thesaid Letters Patent should read as corrected below.

In the grant, lines 1 and 2 and in the heading to the printedspecification line 3, name of second inventor for "Norbert L. Meinert"each occurrence read Norbert Meinert Signed and sealed this 24th day ofNovember 1964o (SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. OPTICAL GLASS WITH HIGH INDEX OF REFRACTION AND SMALL DISPERSIONCONSISTING ESSENTIALLY OF